1. Field of the Invention
The present invention relates to a reaction solution, a set of the reaction solution and an ink, an inkjet recording apparatus and an image recording method, and particularly relates to a reaction solution to be used with an ink when printing is performed on a recording medium, a set of a reaction solution and an ink, and an image recording method using the same.
2. Related Background Art
The inkjet recording method is a method of printing that can achieve printing of high resolution and high quality images at high speed using an inexpensive apparatus, where ink droplets are ejected and attached on a recording medium such as paper.
Japanese Patent Application Laid-Open No. H06-106735A discloses technical means to obtain color images of high quality, high image density and free from color bleed, by using a black ink that thickens or agglomerates reacting with a salt, and a color ink containing the salt. That is, a good image can be obtained by using two liquids in printing: a solution containing a salt and an ink composition reactive with the solution.
Various proposals for using two liquids have been made, for example, in Japanese Patent Application Laid-Open Nos. H09-207424A, 2000-37942A and the like.
Furthermore, Japanese Patent Application Laid-Open No. 2000-94825A discloses use of a polyvalent metal salt and a nonionic resin to thicken the solution containing the polyvalent metal salt so as to fix a coloring material on the surface of paper.
The inventors of the present invention studied ink sets containing polyvalent metal ions to obtain high quality color image of high image density and free from color bleed, and completed the recording method as disclosed in Japanese Patent Application Laid-Open No. H06-106735A, etc. They, however, recognized new problems due to the high reactivity.
Specifically, because of the high reactivity, the reaction is almost completed at the time when a liquid composition and an ink composition come in contact with each other (within about several hundreds msec). Consequently, coloring material components that have reacted with the liquid composition remain on the recording medium which may lead to falling off of the recorded region with rubbing (rub-off), not desirable for both side printing. To solve this problem, a nonionic resin was added to a solution containing a polyvalent metal in Japanese Patent Application Laid-Open No. 2000-94825A, to fix coloring materials on the surface of paper so as to prevent the rub-off problem of the recorded area effectively.
However, when normal paper is coated with a solution containing a polyvalent metal and a nonionic resin by roller coating, uniform coating is difficult because of the low penetrability of the solution into the paper, which may cause unevenness in image density of the recorded image. Readily conceivable means to solve this problem of uneven image density, might be to increase the application amount of the liquid composition, or to increase the coating pressure by controlling the pressure of the coating roller.
However, if a large amount of a solution is applied, the period for drying the printed matter becomes long, and delayed fixation tends to cause smear when the recorded area is rubbed. In addition, the surface of the paper tends to crease because a large amount of solution is applied on the recording medium. Therefore this method is not preferred. On the other hand, if the pressure of the roller is adjusted to increase the coating pressure, a problem arises such that the apparatus becomes complicated to cope with normal paper of different thicknesses, and therefore this method is not preferred like the above method.